Regenerative air brake module

ABSTRACT

An air braking system for a vehicle blends regenerative and foundation braking during low deceleration conditions in an effective and controlled manner. The braking system also includes a mechanical override that bypasses system electronics in response to an aggressive brake request such that treadle circuit pressure is sent directly to a brake relay circuit to actuate vehicle brakes.

TECHNICAL FIELD

This invention generally relates to a regenerative air brake module for a vehicle.

BACKGROUND OF THE INVENTION

Hybrid vehicles include an e-machine or other alternative power source which works in conjunction with an internal combustion engine to drive the vehicle. The vehicle includes traditional foundation braking and regenerative braking can also be provided by the alternative power source.

Hybrid vehicles recapture braking energy that would otherwise be lost as heat through foundation braking to improve vehicle operational efficiency. When regenerative braking is being performed, it is important that the vehicle operator's braking and handling “feel” be unaffected. To achieve this there should be controlled blending of regenerative and foundation braking such that the vehicle operator can operate the vehicle in a normal and predictable manner. Maintaining this feel for hybrid commercial truck braking systems presents even more challenges. Further, it is important that mechanical safety features be incorporated into the system in the event of a failure of the regenerative braking portion of the brake system.

SUMMARY OF THE INVENTION

An air brake system for a vehicle blends regenerative and foundation braking during low deceleration conditions in an effective and controlled manner. The braking system also includes a mechanical override that bypasses system electronics in response to an aggressive brake request such that treadle circuit pressure is sent directly to a brake relay circuit to actuate vehicle brakes.

The air brake system includes a brake input member configured to receive a brake request, the brake input member mechanically actuating a treadle valve of a treadle circuit having a treadle circuit air pressure. A sensor measures the brake request, and a controller is configured to determine a valve command based on the brake request from the sensor and based on a regenerative braking level. A control valve is configured to control a delivered air pressure level in a brake relay circuit based on the valve command, and the brake relay circuit is configured to communicate the delivered air pressure level to a vehicle brake.

In one example embodiment, the air braking system for a vehicle includes a treadle circuit with a treadle valve and a relay circuit with a relay valve. The treadle valve is associated with a treadle input that is actuated in response to a brake request. The relay valve communicates a delivered air pressure to a vehicle brake. A first pressure sensor measures a requested brake pressure from the treadle valve. A control valve is in a normally open position to directly connect the treadle circuit and the relay circuit during a first mode of operation. The control valve is operable to block treadle pressure in a second mode of operation. An electronic pressure regulator is configured to communicate treadle pressure to the relay valve when in the first mode of operation and is configured to communicate an air pressure less than the treadle pressure when in the second mode of operation. A controller is configured to generate a control signal based on the requested brake pressure and an available amount of regenerative braking. The control valve and electronic pressure regulator operate in the first or second mode of operation in response to the control signal to communicate the delivered air pressure to the vehicle brake. A mechanical bypass valve is operable to directly communicate treadle pressure to the relay valve when the requested brake pressure is greater than an override limit.

The first mode of operation is defined as a system “off” mode for standard air brake operation, and the second mode of operation is defined as a system “on” mode for regenerative braking operations at a condition where the requested brake pressure is less than a predetermined limit. When in the first mode of operation, the delivered air pressure is the treadle pressure, and when in the second mode of operation, the delivered air pressure is an air pressure that is less than the treadle pressure.

In one example, the air brake system includes a second pressure sensor that measures a delivered brake pressure to the relay valve and communicates the delivered brake pressure to the electronic control unit to provide a closed-loop system.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a vehicle brake system with a regenerative brake module.

FIG. 2 is a schematic representation of a regenerative brake module as used in the brake system of FIG. 1.

FIG. 3 is the regenerative brake module of FIG. 2 in a system off condition.

FIG. 4 is the regenerative brake module of FIG. 2 in a system on condition.

FIG. 5 is the regenerative brake module of FIG. 2 in an aggressive braking condition.

FIG. 6 is another example of a regenerative brake module that can be used in the brake system of FIG. 1.

FIG. 7 is another example of a regenerative brake module shown in a standard brake operation mode.

FIG. 8 is the regenerative brake module of FIG. 7 in a lower pressure, regenerative brake operation condition.

FIG. 9 is the regenerative brake module of FIG. 7 in a mid-pressure, regenerative brake shutdown sequence.

FIG. 10 is the regenerative brake module of FIG. 7 in high pressure, regenerative brake override condition.

FIG. 11 is a schematic representation of a bypass valve combining stage one and stage two valves that can be used in a regenerative brake module as shown in FIGS. 7-10.

FIG. 12 is the bypass valve of FIG. 11 with a pressure regulator blocked condition and with stage one closed, which corresponds to FIG. 9.

FIG. 13 is the bypass valve of FIG. 11 with a pressure regulator blocked condition and with the stage two valve open to provide a bypass flowpath as shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A braking system 10 for a hybrid vehicle includes a primary brake circuit 12 for a rear axle 14 and a secondary brake circuit 16 for a front axle 18. The exemplary hybrid vehicle includes a drive system with an electric motor and combustion engine that cooperate to propel the vehicle; however, in alternate embodiments other hybrid vehicles (for example, hydraulic hybrids and spinwheel hybrids), and electric vehicle configurations may utilize the brake circuit described herein. The rear axle 14 includes a set of rear wheels 20 and the front axle 18 includes a set of front wheels 22. Each wheel 20, 22 includes a wheel brake with an air chamber 24. A front air supply reservoir 26 is fluidly connected to front air chambers 24 via fluid connections in the secondary brake circuit 16. A rear air supply reservoir 28 is fluidly connected to rear air chambers 24 via fluid connections in the primary brake circuit 12. An air dryer 30 is connected to the front 26 and rear 28 air supply reservoirs to reduce the moisture content of the air being supplied to the reservoirs.

A control valve 32 is fluidly connected to the primary 12 and secondary 16 brake circuits. The control valve 32 can also be optionally fluidly connected to a tractor protection valve 34 and trailer brake system 36. A brake input member, such as a brake treadle 38 for example, is connected to the primary 12 and secondary 16 brake circuits, as well as being connected to the control valve 32. A vehicle operator can press down on the brake treadle 38 to initiate a braking request. The braking system 10 may also include a separately actuated parking brake 40 that can be selectively actuated by the vehicle operator.

The braking system 10 includes a regenerative brake module 50 for each of the front 18 and rear 14 axles. The regenerative brake module 50 for the rear axle 14 is associated with a rear relay valve 52 that is part of a brake relay circuit. The regenerative brake module 50 for the front axle 18 is the same as the module for the rear axle; however, the brake module 50 additionally includes a front relay valve 54 not present in the exemplary secondary brake circuit 16.

One example of the regenerative brake module 50 is shown in greater detail in FIGS. 2-6. As shown in FIG. 2, the brake treadle 38 forms part of a treadle circuit that includes a first treadle valve 56 for the primary brake circuit 12 and a second treadle valve 58 for the secondary brake circuit 16. In the example shown, a regenerative brake module 50 for the rear axle 14 is shown, with the first treadle valve 56 being fluidly connected to the rear air supply reservoir 28. It should be understood that operation of the regenerative brake module 50 for the front axle 18 would be the same as shown for the rear axle but would be connected through the second treadle valve 58.

A first pressure sensor 60 measures a requested brake pressure generated by the vehicle operator pressing down on the brake treadle 38. A control valve comprising a 3/2 valve 62 for example, is downstream of the first pressure sensor 60. The 3/2 valve 62 is in a normally open position and is operable to move to a closed position to block airflow to vehicle foundation brakes, i.e. to block direct flow to the rear relay valve 52. An electronic pressure regulator valve 64 connects to the 3/2 valve 62 when in the closed position to allow venting. The electronic pressure regulator valve 64 provides a fluid connection between the rear air supply reservoir 28 and the rear relay valve 52 positioned upstream of the rear air chambers 24.

An electronic control unit 66 receives the vehicle operator brake pressure request, i.e. a treadle pressure input signal 68, and compares the requested brake pressure to an available amount of regenerative brake torque that can be provided by an alternative power source 70, such as an electric generator for example. A determination of available regenerative braking can take into account parameters such as vehicle speed, passenger ride preference, the brake request, the regenerative capacity of the vehicle, energy storage state-of-charge or equivalent, and various powertrain and engine characteristics. Although an exemplary embodiment is described in which the electronic control unit 66 determines an ‘available regenerative braking’ it is to be understood the electronic control unit can determine a target regenerative braking level based on based on vehicle parameters that is less the maximum available regenerative braking level and control the vehicle based on the target regenerative braking level. For example, the target regenerative braking level may be less than the available regenerative braking during transient conditions such as a shift event. The electronic control unit 66 can determine an amount of foundation brake pressure based on the available regenerative braking level, for example to supplement regenerative braking to generate a desired total brake torque. The electronic control unit 66 generates a control signal based on the determined foundation brake level to command the 3/2 valve 62 to the closed position thereby connecting the electronic pressure regulator valve 64 to the reservoir and providing desired foundation brake pressure needed to the rear relay valve 52 of the brake relay circuit.

In one example, a vehicle operator generates a brake request measured by the first pressure sensor at 30 psi. The electronic control unit 66 determines how much total braking torque is being requested by translating the pressure signal to a brake torque output, for example 1000 Nm by modeling or using a lookup table. The control unit 66 determines the available regenerative braking torque and determines a supplemental foundation brake level based on the brake torque output and the available regenerative braking torque. This torque requirement is translated back to a reduced brake application pressure by the electronic control unit 66 and is delivered by the pressure regulator 64 from the reservoir to the wheel brakes via relay valve 52 and the air chambers 24. For example, if the request is 1000 Nm and the available regenerative torque is 200 Nm, then the foundation brakes will supply the remaining 800 Nm. The calculation of total brake torque versus treadle pressure requires a known number of braking units and does not take into account trailer brakes, which comprise a variable braking source. Application of this regenerative brake module 50 to the trailer brake air circuit would also be possible if the number of trailer brakes were determined.

At least one pressure-piloted valve 72 selectively provides fluid communication between the treadle 38 and the relay valve 52 when the requested brake pressure is greater than a predetermined (override) value limit, i.e. a mechanical bypass is provided to quickly and efficiently accommodate aggressive braking requests. In one example, a second pressure sensor 86 is included that measures a delivered brake pressure to the relay valve and communicates the delivered brake pressure to the electronic control unit 66 to provide a closed-loop system.

Thus, the first pressure sensor 60, second pressure sensor 86, the 3/2 valve 62, the pressure-piloted valve 72, the electronic pressure regulator valve 64, and the electronic control unit 66 cooperate to form the regenerative brake module 50. The regenerative brake module 50 is switchable between a system “off” condition and a system “on” condition depending on various factors such as an amount of braking requested, vehicle speed, road conditions, etc.

FIG. 3 shows an example of the regenerative brake module 50 being in the system off condition For example, the control module can determine and command the system off condition when a stability control event (ABS, traction control, etc.) is detected, at slow speed, when the energy storage devices are at a maximum state of charge, or when a system fault is detected. In the system off condition the 3/2 valve 62 is normally open such that air can flow through the 3/2 valve 62, to the pressure regulator 64, and to the relay valve 52 (as indicated by flowpath 74). At pressures that exceed the predetermined limit, the pressure piloted valve 72 opens a secondary flowpath 76 to fluidly connect the pressure to the relay valve 52. In the off state both flowpaths are available depending on the treadle pressure. The pressure regulator valve 64 is connected to the supply reservoir 28 as indicated at 78. Thus, in this system off condition, there is standard air brake operation with all electronic valves being normally open for control pressure and a mechanical bypass valve being normally closed but which can provide a secondary flow path in response to pressures exceeding a predetermined limit.

FIG. 4 shows the system on condition, which typically corresponds to a situation where low pressure (pressure below the predetermined limit) braking is requested. In the system on condition (regenerative braking active) the treadle pressure is blocked by the 3/2 valve 62 and the electronic control unit 66 reads this treadle pressure as a braking request. The electronic control unit 66 then generates a command signal which is communicated to the pressure regulator 64 to provide an alternate pressure, i.e. the control unit 66 modifies the treadle circuit request.

When this occurs, the 3/2 valve 62 is moved to the closed position, as shown in FIG. 4, to block air flow from the treadle circuit and to open an exhaust path 82 through the pressure-piloted valve 72 for the electronic pressure regulator 64 to utilize during delivery of the pressure required by the electronic control unit 66. The electronic pressure regulator valve 64 delivers pressure from the reservoir connection 78 to the relay valve 52. The pressure-piloted valve 72 remains closed in this condition to isolate the requested treadle pressure from the pressure signal delivered by the electronic pressure regulator 64.

A second pressure sensor 86 is positioned downstream of the pressure regulator valve 64 and upstream of the relay valve 52 to measure the pressure being delivered to the relay valve 52. Thus, in the system on condition a commanded pressure is delivered from the supply reservoir 28 via the electronic pressure regulator 64 to the relay valve 52, a vent path is provided for the pressure regulator valve 64, and the delivered brake pressure is monitored by the second pressure sensor 86 to provide closed loop control. Further, in the event of a full holdoff, the air brakes can be “prepped” at a crack pressure.

FIG. 5 shows the regenerative brake module 50 in a “push through” braking condition, which would occur during a high pressure (above predetermined pressure limit) braking event, i.e. aggressive or panic stopping. In response to an aggressive braking request, the electronic control unit receives the high pressure signal from the pressure sensor 60 and cancels regenerative braking operation, returning the 3/2 valve to its normally open position, and communicates the treadle pressure through the electronic pressure regulator 64 to the relay valve 52. In addition, the pressure-piloted valve 72 moves to a secondary position where air flow is communicated through the pressure-piloted valve 72 to a location downstream of the electronic pressure regulator valve 64 (as indicated by flowpath 88). Further, air flow venting from the 3/2 valve 62 is blocked by the pressure-piloted valve 72 (as indicated at 90) such that all available pressure generated by the treadle is communicated directly to the relay valve 52. The redundant operation of blocking the exhaust port serves to alleviate any inadvertent venting of the treadle pressure if the system could not react fast enough during a panic stop or failed to cancel the regenerative braking mode for some reason.

Thus, if the system is in the “on” condition and a vehicle operator initiates a panic stop, the treadle pressure overpowers the pressure-piloted valve 72 and the pressure-piloted valve 72 blocks the vent option of the pressure regulator valve 64. In other words, in this situation the treadle pressure signal overrides electronic control and the treadle pressure is sent directly to the relay valve 52. As discussed above, the second pressure sensor 86 measures the delivered brake pressure supplied to the relay valve 52 and communicates the delivered brake pressure to the electronic control unit 66 to provide a closed-loop system. If the first pressure sensor 60 or the second pressure sensor 86 reads a pressure in excess of the predetermined limit, i.e. the pressure limit of the pressure-piloted valve 72, when the pressure-piloted valve 72 is moved to the bypass position, the pressure sensor 86 communicates the pressure data to the electronic control unit 66 to cancel the control (system on) mode and revert to a system off condition.

The regenerative brake module 50 also incorporates a fault sensing condition. During normal operation, when the system is in the off condition, the first 60 and second 86 pressure sensors read the same pressure. If the sensors read different pressures, this can be used to detect possible valve failures. If one of the sensors fails, for example if the treadle pressure sensor (first pressure sensor 60) fails, the second pressure sensor 86 would still be capable of reading the requested pressure. Any difference between a failed delivery sensor and the pressure regulator valve 64 (associated with the second pressure sensor 86) can be used in a perturbation test to determine a cause of the failure. As such, a double component failure is required to lose each brake circuit operation.

FIG. 6 shows another example of a regenerative brake module 50′. This configuration is similar to that of FIGS. 2-5; however, the pressure-piloted valve 72 is separated into two pressure control valves. A first pressure piloted valve 100 is operable to bypass the 3/2 valve 62 when pressure exceeds a first predetermined limit, which would occurring during an event as described above with regard to FIG. 4 or 5. A second pressure-piloted valve 102 is operable to block pressure from exhausting from the 3/2 valve 62 when pressure exceeds a second predetermined limit, which would occur during an aggressive braking request as described above with regard to FIG. 5. The first and second predetermined limits are set to a common pressure which would be within the range of 20-50 psi, for example.

In an optional embodiment, the brake module 50 can include an additional check valve, schematically indicated at 80. This valve 80 would be operational only during a failure mode as described below. In the system “on” condition, if the pressure regulator 64 fails to switch off when treadle pressure exceeds the override limit, i.e. when the bypass valve is tripped, then there is a condition where two pressure regulators would be fighting for control. For this reason, the valve 72 is configured to block the exhaust path such that the valve does not allow the pressure regulator 64 to vent treadle pressure back to the control unit's commanded value, i.e. a lower pressure.

However, the valve may still attempt to ventilate. In a situation where treadle pressure exceeds the override limit and continues to increase, the pressure regulator 64 may try to vent what is considered to be excessive downstream pressure, which fills the blocked vent air passage with high pressure air. As treadle pressure begins to decrease, but is still higher than the override limit, the high pressure air is still trapped behind the pressure regulator 64. This results in application of an unbalance load on the pressure regulator valve 64 and serves as a mechanical mechanism to request more pressure from the regulator. The result is that the regulator will start to deliver pressurized air from the reservoir as pressure from the treadle is decreasing, causing a backflow through the treadle. Adding the check valve 80 allows this pressure to escape in this failure state and prevents backflow. If the check valve 80 is not included, the system may have a lag in brake release timing if the control unit 66 does not properly cancel out of the regenerative braking mode in this particular failure mode.

Another example of a regenerative brake module 200 is shown in FIGS. 7-10. This configuration is similar to that of FIGS. 2-5; however, the mechanical bypass, i.e. the pressure-piloted valve 72 comprises a valve 202 that includes a stage one valve 204 and a stage two valve 206.

FIG. 7 shows a configuration that corresponds to a system “off” mode which occurs during standard braking operations. In this mode, the 3/2 valve 62 is in a normally open position and fluidly connected to the relay valve 52 through the pressure regulator valve 64, which is also in a normally open position. As such, treadle pressure from a treadle circuit is communicated directly to the relay valve 52 in a relay circuit of the brake system to allow standard braking to occur in response to braking requests input to the treadle 38.

FIG. 8 shows a configuration for a system “on” condition that comprises a first mode of operation. This first mode of operation is for braking requests that comprise a low pressure condition, i.e. requested pressures are below a predetermined limit such as 20-50 psi for example. In this mode of operation, the 3/2 valve 62 is moved to a position that blocks treadle pressure and opens an exhaust path 210 for the 3/2 command valve to the stage one valve 204. As such, air can be exhausted through the regulator valve 64, through the 3/2 valve 62 and out through the stage one valve 204. The stage two valve 206 continues to block access to the treadle circuit.

The first pressure sensor 60 reads the command pressure, i.e. the pressure requested as a result of an input to the treadle 38, and communicates this pressure to the electronic control unit 66. The control unit 66 determines how much regenerative braking can be supplied and then determines how much air pressure to deliver from the reservoir 28 to supply any remaining pressure needed. As such, the requested pressure, instead of being wholly supplied via the reservoir as occurs in standard operation, is supplied as a combination of regenerative braking and a reduced amount of reservoir air pressure. Thus, the air pressure delivered to the relay valve 52 is less than the command pressure. The second pressure sensor 86 measures the pressure supplied to the relay valve 52 and communicates this measured pressure back to the control unit 66 to establish a closed loop control of delivery pressure.

FIG. 9 shows another mode of operation that corresponds to a mid-pressure, regenerative brake shutdown sequence. This occurs at pressures that exceed the predetermined pressure limit set for the FIG. 8 configuration, but which are less than an override limit that would be set for a panic or aggressive brake request such as that which will be discussed with regard to FIG. 10.

In the mid-pressure mode of operation, initially the 3/2 valve 62 blocks the treadle pressure and the stage two valve 206 is also in a blocking position. The stage one valve 204 also moves to a blocking position to block the exhaust path 210 from the regulator valve 64 and 3/2 valve 62. Initially, the braking supplied to the wheel 20 is a blend of regenerative braking and a reduced air pressure, i.e. reduced compared to the command request, from the reservoir. However, in this mode, the control unit 66 blends out the regenerative braking such that the system will revert to the “off” mode as shown in FIG. 7 for standard brake operation. Thus, the 3/2 valve 62 will move from the blocking position shown in FIG. 9 back to a normally open position.

FIG. 10 shows a second mode of operation that corresponds to a high pressure, regenerative brake override condition. This would occur for a panic braking or aggressive braking request. In this configuration the stage one valve 204 blocks the exhaust path 210 and the stage two valve 206 moves to an open position, i.e. a bypass position, to directly connect the treadle circuit to the relay circuit, i.e. treadle pressure is directly supplied to the relay valve 52. The control unit 66 has no capability to override the treadle pressure and the system returns to the “off” mode as shown in FIG. 7.

In an optional embodiment, the brake module 200 can include an additional check valve, schematically indicated at 212. This valve 212 would be operational only during a failure mode as described below. In the system “on” condition, if the pressure regulator 64 fails to switch off when treadle pressure exceeds the override limit, i.e. when the bypass valve 202 is tripped, then there is a condition where two pressure regulators would be fighting for control. For this reason, the stage one valve 204 is configured to block the exhaust path 210 such that the valve does not allow the pressure regulator 64 to vent treadle pressure back to the control unit's commanded value, i.e. a lower pressure.

However, the valve may still attempt to ventilate. In a situation where treadle pressure exceeds the override limit and continues to increase, the pressure regulator 64 may try to vent what is considered to be excessive downstream pressure, which fills the blocked vent air passage with high pressure air. As treadle pressure begins to decrease, but is still higher than the override limit, the high pressure air is still trapped behind the pressure regulator 64. This results in application of an unbalance load on the pressure regulator valve 64 and serves as a mechanical mechanism to request more pressure from the regulator. The result is that the regulator will start to deliver pressurized air from the reservoir as pressure from the treadle is decreasing, causing a backflow through the treadle. Adding the check valve 212 allows this pressure to escape in this failure state and prevents backflow. If the check valve 212 is not included, the system may have a lag in brake release timing if the control unit 66 does not properly cancel out of the regenerative braking mode.

FIGS. 11-13 show the bypass valve 202 as used in the configuration shown in FIGS. 7-10. This valve is also set forth and described in co-pending application Ser. No. ______, filed on even date herewith and assigned to the same assignee as the present invention, which is directed to the air braking system. The subject matter of Ser. No. ______ is herein incorporated by reference. The bypass valve 202 incorporates the stage one 204 and stage two 206 valves as discussed above.

The bypass valve 202 has a valve body 214 that includes a bore 216 that receives the stage one 204 and stage two 206 valves. The bore 216 has an enlarged bore portion 216 a of a maximum bore diameter at one valve end. A first reduced bore portion 216 b extends from the enlarged bore portion 216 a to a second reduced bore portion 216 c. The stage one valve 204 is normally open and the stage two valve 206 is normally closed. The valve body 214 includes a 3/2 valve port 222, a relay valve port 224, a treadle port 226, and an exhaust port 228 that exhaust out of the enlarged bore portion 216 a.

A shaft 230 is fit within the valve body 214 in a sliding relationship and extends between a first shaft end 232 and a second shaft end 234. A bore 236 is formed within the shaft 230 and extends from the first shaft end 232 to the second shaft end 234. Fit within the bore 236 is a tube 238 that receives a plunger 240 at the first shaft end 232. The plunger 240 has a stem or shaft portion that is slidingly received within the tube 238 and an enlarged head portion that extends out of the tube 238. A seal 242 is received around the shaft portion and abuts against an underside of the enlarged head portion.

In the configuration shown in FIG. 11, the system is in a low pressure mode such as that described above with regard to FIG. 8. The first shaft end 232 is seated against a first valve seat 244 formed at one end of the second reduced bore portion 216 c and the plunger 240 is positioned such that the seal 242 is moved out of engagement with the shaft 230 to allow the pressure regulator 64 to connect to the exhaust path 210 via port 222.

The shaft 230 also includes an enlarged flange portion 246 that supports a sealing member 248 for engagement with a second seal seat 250 formed at the transition between the first reduced bore portion 216 b and the second reduced bore portion 216 c. A resilient member 252 has one end 254 supported on a side of the flange portion 246 that is opposite of the sealing member 248 and an opposite end 256 that is seated against an insert member 258 that is fit within the enlarged bore portion 216 a. The insert member 258 comprises a cup-shaped member having a base portion with an opening 260 through which the second shaft end 234 extends. A surface of the base portion surrounding the opening 260 provides a seat of the end 256 of the resilient member 252.

Received within the insert member 258 is a piston 262 that also comprises a cup-shaped member. A piston head portion 264 of the piston 262 faces the base portion of the insert member 258 and includes an opening 266 to receive the tube 238. A stem 268 surrounds the opening 266 and extends outwardly from the piston head portion 264 in a direction away from the base portion of the insert member 258. The tube 238 extends through the stem 268.

An end cap 270 is fit against the valve body 214 at an open end of the enlarged bore portion 216 a. The end cap 270 includes an opening 272 for the exhaust path 210. Surrounding the opening 272 is a lip 274 that extends inwardly toward the piston 262. A resilient member 276 is seated within the piston 262. One end 278 of the resilient member 276 is seated against the piston head portion 264 and an opposite end 280 of the resilient member 276 is seated against end cap 270 to surround the lip 274.

As discussed above, FIG. 11 discloses a low pressure mode for the brake system. The 3/2 valve port 222 is open such that the pressure regulator 64 is free to use the exhaust path through the tube 238 and out the exhaust port 228. As shown, the plunger 240 is moved out of engagement with the shaft 230 to open the exhaust path and the relay valve port 224 is blocked. The treadle port 226 that is connectable to the treadle circuit is inactive at low braking pressures. As such, the valve design provides a balanced configuration where performance is independent of the downstream relay valve pressure.

In FIG. 12, the valve 202 is in a position that corresponds to the mode set forth in FIG. 9. The plunger 240 is sealingly seated within the tube 238 and shaft 230 such that the pressure regulator 64 is blocked at the 3/2 valve port 222 from allowing exhaust flow out of port 228. As such, the pressure regulator 64 is blocked from lowering the brake pressure and the control unit 66 is configured to blend out of the regenerative braking to return to standard brake operation. As shown, the stage one valve 204 has closed and the piston 262 has moved away from the insert 258. This mode would occur at pressures that exceed a predetermined limit that would be within the range of 20-50 psi, for example.

In FIG. 13, the valve 202 is in a position that corresponds to the mode set forth in FIG. 10. The exhaust path is blocked via the plunger 240 at the 3/2 valve port 222. The piston 262 has moved further away from the insert 258, and the flange portion is unseated from the second valve seat 250. This connects the treadle circuit directly to the relay circuit for an aggressive braking condition via the relay valve port 224 and the treadle port 226. The electronic valves are therefore immediately bypassed and the control unit 66 cannot override the bypass valve 202 in this condition.

As shown and discussed, the various movements of the valve components occur in stages. The second stage 206 is normally closed, but as treadle pressure increases the valve is configured initially move the piston 262 away from the shaft end 234 to first blend out regenerative braking at mid-pressure ranges. As treadle pressure increases for an aggressive braking request, the shaft 230 is free to move the flange portion 246 away from the second valve seat 250 due to the compressed movement of the piston 262. This directly connects the relay and treadle circuits.

The subject braking system 10 operates to provide computer controlled brake blending while maintaining appropriate mechanical safety features. As discussed above, brake treadle pressure is read by a pressure sensor and when the system is in the on condition, the pneumatic signal generated by the vehicle operator is blocked by the 3/2 valve, which is normally open. This valve simultaneously opens an exhaust/vent port for the proportional regulator valve that sends an alternative pressure command to the brake system. The regulator valve taps directly into the supply reservoir and delivers the alternate pressure signal from this supply. The second pressure signal reads the output pressure signal and closes the control loop on the delivery brake pressure. An alternative mechanical bypass exists that opens a self-piloted valve at a predetermined pressure to mechanically limit the regenerative braking zone to a lower range of the brake application range. This keeps regenerative operation in a low-g arrangement and voids vehicle dynamic influences.

In one example, two regenerative brake modules are used on each circuit in the vehicle. The redundancy of the two modules allows cross checking of the input pressure sensor. Examining both pressure sensors in each circuit can determine if there is a valve failure in-between, and a perturbation of the valve setting can examiner the delivery sensor function. This module can also provide ATC operation in place of an ATC valve.

Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention. 

1. An air braking system for a vehicle comprising: a brake input member configured to receive a brake request, the brake input member mechanically actuating a treadle valve of a treadle circuit having a treadle circuit air pressure; a sensor that measures the brake request at the treadle circuit; a controller configured to determine a control valve command based on the brake request from the sensor and based on a regenerative braking level; and a control valve configured to control a delivered air pressure level in a brake relay circuit based on the control valve command, wherein the brake relay circuit is configured to communicate the delivered air pressure level to a vehicle brake.
 2. The air braking system according to claim 1 wherein the controller is configured to determine the brake request based on treadle valve pressure.
 3. The air braking system according to claim 1 wherein the controller is configured to: receive a pressure signal measured in the treadle circuit, to determine an available regenerative braking level, and to determine the control valve command based on the pressure signal and the available regenerative braking level.
 4. The air braking system according to claim 1 wherein, when operating in a first mode, the controller commands pressure to vehicle brakes at a different pressure than that requested by the treadle valve such that regeneration compensates for at least a portion of the brake request.
 5. The air braking system according to claim 4 wherein, when operating in a second mode, air flows directly between the treadle circuit and the brake relay circuit to allow direct control of the delivered air pressure level by treadle valve pressure.
 6. The air braking system according to claim 1 wherein, when treadle circuit air pressure falls below a predetermined pressure, the control valve allows direct air flow between the treadle circuit and the brake relay circuit.
 7. The air braking system according to claim 1 wherein direct air flow is provided between the treadle circuit and the brake relay circuit in response to a system fault detection or when a high deceleration brake request.
 8. The air braking system according to claim 1 wherein the regenerative braking level is based at least on one or more of the following parameters including vehicle speed, brake request, energy storage state-of-charge, and engine characteristics.
 9. An air braking system for a vehicle comprising: a treadle circuit including a treadle valve associated with a treadle input that is actuated in response to a brake request; a first pressure sensor that measures a requested brake pressure from the treadle valve; a relay circuit including a relay valve that communicates a delivered air pressure to a vehicle brake; a control valve in a normally open position to directly connect the treadle circuit and the relay circuit during a first mode of operation, and wherein the control valve is operable to block treadle pressure in a second mode of operation; an electronic pressure regulator configured to communicate treadle pressure to the relay valve when in the first mode of operation and configured to communicate an air pressure less than the treadle pressure when in the second mode of operation; a controller configured to generate a control signal based on the requested brake pressure and an available amount of regenerative braking, the control valve and electronic pressure regulator operating in the first or second mode of operation in response to the control signal to communicate the delivered air pressure to the vehicle brake; and a mechanical bypass valve that is operable to directly communicate treadle pressure to the relay valve when the requested brake pressure is greater than an override limit.
 10. The air braking system according to claim 9 wherein: when in the first mode of operation, the delivered air pressure is the treadle pressure; and when in the second mode of operation, the delivered air pressure is an air pressure that is less than the treadle pressure.
 11. The air braking system according to claim 10 wherein the first mode of operation comprises a system “off” mode for standard air brake operation and wherein the second mode of operation comprises a system “on” mode for regenerative braking operations at a condition where the requested brake pressure is less than a predetermined limit.
 12. The air braking system according to claim 11 wherein the bypass valve is in a closed position when operating in the first mode of operation, and wherein the bypass valve is moveable to provide an exhaust path when in the second mode of operation such that air can be exhausted through the electronic pressure regulator, through the control valve, and out of the bypass valve.
 13. The air braking system according to claim 12 including a second pressure sensor that measures the delivered air pressure to the relay valve and communicates the measured delivered air pressure to the controller to provide closed loop control.
 14. The air braking system according to claim 12 wherein the predetermined limit comprises a low pressure condition and including a third mode of operation where the requested brake pressure is greater than the predetermined limit and less than the override limit to comprises a mid-pressure operating condition, and wherein, when in the third mode of operation, the bypass valve is configured to block the exhaust path and the controller is configured to blend out regenerative braking to revert back to the first mode of operation.
 15. The air braking system according to claim 13 wherein when the requested brake pressure is greater than the override limit the bypass valve is configured to block the exhaust path and directly connect the treadle pressure at a location upstream of the control valve to the relay valve at a location that is downstream of the electronic pressure regulator.
 16. The air braking system according to claim 9 wherein in response to a system fault detection the treadle pressure is communicated directly to the relay valve.
 17. A method of controlling an air brake system for a vehicle comprising: initiating a brake request by actuating a treadle input associated with a treadle valve in a treadle circuit; measuring a requested brake pressure from the treadle valve with a first pressure sensor; providing a relay valve circuit to communicate a delivered air pressure to a vehicle brake via a relay valve; providing a control valve that is in a normally open position to directly connect the treadle circuit and the relay circuit during a first mode of operation; configuring the control valve to block treadle pressure in a second mode of operation; configuring an electronic pressure regulator to communicate treadle pressure to the relay valve when in the first mode of operation, and to communicate an air pressure less than the treadle pressure when in the second mode of operation; generating a control signal based on the requested brake pressure and an available amount of regenerative braking, with the control valve and electronic pressure regulator operating in the first or second mode of operation in response to the control signal to provide the delivered air pressure; communicating the delivered air pressure to the vehicle brake via the relay valve; and directly communicating treadle pressure to the relay valve when the requested brake pressure is greater than an override limit via a mechanical bypass valve.
 18. The method according to claim 17 wherein, when in the first mode of operation, the delivered air pressure is the treadle pressure, and when in the second mode of operation, the delivered air pressure is an air pressure that is less than the treadle pressure and including: defining the first mode of operation as a system “off” mode for standard air brake operation; and defining the second mode of operation as a system “on” mode for regenerative braking operations at a condition where the requested brake pressure is less than a predetermined limit.
 19. The method according to claim 18 including closing the bypass valve when operating in the first mode of operation, and moving the bypass valve to provide an exhaust path when in the second mode of operation such that air can be exhausted through the electronic pressure regulator, through the control valve, and out of the bypass valve.
 20. The method according to claim 19 including measuring the delivered pressure to the relay valve with a second pressure sensor, and communicating the measured delivered pressure to the controller to provide closed loop control.
 21. The method according to claim 20 wherein the predetermined limit comprises a low pressure condition and including a third mode of operation where the requested brake pressure is greater than the first predetermined limit and less than the override limit to comprise a mid-pressure operating condition, and including: blocking the exhaust path via the bypass valve when in the third mode of operation; and blending out regenerative braking to revert from the third mode of operation to the first mode of operation. 